We plan to continue my X-Ray crystallographic investigations of the molecular structures of membrane lipids with the specific aim of understanding how these lipids contribute to the structure and function of Biological Membranes. The first steps in this study have just been completed by crystalizing and solving the 3-dimensional molecular structure of a low temperature form of dimyristoyl L alpha-phosphatidylcholine dihydrate. This form crystallizes from the solvent system between 0 degrees C and 22 degrees C. In the proposed project we plan to investigate the high-temperature form which grows from the same solution. The knowledge of several conformational forms of Lecithin will aid in understanding structural aspects of the lipid portion (i.e., the portion which is most responsible for flexibility and 2-dimensional structure) of most biological membranes. Lecithin is the most prevalent lipid in many biological membranes. The proposed study will have 4 parts; 1. finish the details of the current structure determination. (The present residual factor is 17.4% and is expected to go to 14%.) 2) grow the high temperature crystal form of this Lecithin and solve its molecular structure. 3) grow crystals of other chemical forms of Lecithin, particularly those containing unsaturated hydrocarbon chains and to solve these molecular structures. This portion of the plan will include looking for other hydration states of the crystals. 4) investigate why the direct methods of crystallographic structure solving have failed to solve the structure mentioned in part 1) of this plan and to develop a strategy for using these methods for other long-chain compounds, particularly for use in carrying out parts 2) and 3) of this plan. This investigation will be carried out in consultation with Dr. H. Hauptman and Dr. D. Langs of the Medical Foundation of Buffalo.